The proposed radiobiological experiments will extend present knowledge of the action of hyperthermia alone and in combination with ionizing radiation in an effort to answer current questions on the use of this combined modality in cancer therapy. Abundant laboratory data show that radiation sensitivity is markedly enhanced at elevated temperatures This research addresses the need to transform these significant laboratory results into the realm of clinical applicability. Its objectives are: 1) to develop and evaluate a technique of microwave heating of animals and animal tumor systems which are clinically relevant; 2) to assess the relative thermal sensitivities and radiosensitivities of normal and malignant tissues under microwave induced hyperthermic conditions and 3) to compare results with existing experimental data generated in this laboratory in which elevated temperatures were obtained by tumor immersion in water baths. Localized and generalized hyperthermia, as an adjunct to radiotherapy, offers the potential of further increasing rates of local tumor control. The combination of hyperthermia and ionizing radiation as an anti-tumor agent has been under active study in this laboratory since 1968. The principal investigator organized the first International Conference on Cancer Therapy by Hyperthermia and Radiation which was held in April 1975. Over 175 participants of various disciplines attended this meeting which was sponsored by the American College of Radiology and the National Cancer Institute.